Unfortunately Becomeroot never made it to gregale/extras. It was always in http://eko.one.pl/maemo/ Distribution gregale Components user. The person who runs eko.one.pl decided to close down the gregale repository on the site and only leave up bora (OS2007).

However, since becomeroot is, I believe merely a shell script that updates a specific file, you can use the above information to add the above bora repository and install becomeroot from there. After installing becomeroot, you can disable the repository to make sure you don't accidentally "upgrade" to applications and libraries than can't be used in gregale.

Or maybe you can just download the deb and install it from the device itself.

For 2008HE (chinook/diablo) you can use rootsh. It does the same thing as becomeroot (and more).

Also if you know which file becomeroot updates and you have ssh access to root, you can update the file yourself. Use the ancient versions of the "how do I become root" wiki pages for information on what file needs updating and how. As I recall it involves removing an if statement that checks to see if the device is in r&d mode.